Teratogenicity of 27.12-MHz radiation in rats is related to duration of hyperthermic exposure.

Five groups of pregnant Sprague-Dawley rats were either sham exposed or were irradiated in a 27.12-MHz radiofrequency (RF) field at 55 A/m and 300 V/m on gestation day 9. The absorbed power (approximately 11 W/kg) caused a relatively rapid increase in the rat's colonic temperature. Rats in group I were sham irradiated for 2.5 h at 0 A/m, 0 V/m. In group II RF irradiation was terminated after the rat's colonic temperature reached 41.0 degrees C. In group III the 41.0- degrees C temperature was maintained an additional 2 h by manually varying the incident field strength. In group IV irradiation was terminated after the rat's colonic temperature reached 42.0 degrees C. In group V the 42.0- degrees C temperature was maintained an additional 15 min by varying the field strength. At both temperatures the teratogenic and embryotoxic effects of the RF-induced hyperthermia increased as the exposure duration increased, but the increase was especially noticeable at 42.0 degrees C. The results indicate that the teratogenic and embryotoxic effects of RF-induced hyperthermia are related to both the temperature of the dam during exposure and the length of time the dam's temperature remains elevated.